Britain and the US must not be “imprisoned” by the experience of war in Iraq and cannot focus on domestic problems at the expense of their overseas responsibilities, David Miliband has warned.

Speaking after British intervention in Syria was effectively thwarted by his brother Ed, the former foreign secretary said there were “huge risks” to Western retreat from international engagement.

“I believe very profoundly that in an interdependent world, you have to do domestic policy, but you have to do foreign policy as well,” he told The Daily Telegraph.

Mr Miliband, now the president of the International Rescue Committee, stopped short of calling for war on Bashar al-Assad’s regime to end a civil war that has killed more than 100,000 people. “We’ve got people on the ground, not just in Syria but in Turkey, Lebanon, Jordan and Iraq,” he told a foreign policy discussion in Manhattan. “I’ve got people who are in danger.”

However, in attempting to sum up “what I believe without crossing the line”, he quoted Frederick The Great, saying: “Diplomacy without weapons is like music without instruments”.